N/A
N/A
This invention pertains to Kerr effect magnetometry in general, and in particular to a system and method for realizing multi-dimensional or vector Kerr effect magnetometry.
The Magneto-optic Kerr effect (MOKE), or more simply referred to as the Kerr effect, corresponds to a change in the intensity or polarization state of light reflected from a magnetic material. Since the amount of change in the polarization state or intensity is proportional to the magnetization in the material, it is possible to use this effect to examine magnetic properties of a material sample.
The prior art has provided three discrete geometries for characterizing a material sample: longitudinal MOKE; transverse MOKE; and polar MOKE. With a longitudinal MOKE geometry, a magnetic field is applied parallel to the plane of the film and the plane of incidence of the light. With a transverse MOKE geometry, the magnetic field is applied perpendicular to the plane of incidence of the light. With a polar MOKE geometry, the magnetic field is applied orthogonal to the surface of the sample. In all cases, a polarization rotation in the detected light provides an indication of the relative magnetization of the sample under test.
Another prior art approach employed for characterizing light transmissive materials is a polar Faraday effect system. A magnetic field is applied parallel to the surface of the material under test. Light is emitted through a point in the material under test and is received on the opposite side of the material. Intensity or polarization changes in the received light are used to characterize the response of the material to the applied field. Practically speaking, the detector can be located in any location as long as the appropriate optics are employed for relaying the received light.
Systems employing the longitudinal, transverse or polar geometries may be referred to as scalar systems. Scalar analysis has to-date provided the only non-contact, non-destructive approach for detecting magnetic response.
Certain magnetic materials are described as being anisotropic, in that the magnetic response to an applied magnetic field at a point on the surface of the material varies in theta about the point, theta being defined in the plane of the material sample. In general, anisotropic materials exhibit a variation on magnetic behavior in one or multiple directions some of which may or may not be in the plane of the sample. Thus, in the presence of a magnetic field applied in the x direction, a material sample may exhibit one characteristic response in light reflected off the sample in a plane parallel to the x direction, while exhibiting a different characteristic response in light reflected off the sample in a plane parallel to the y direction.
In order to measure the degree of anisotropy of a sample using scalar Kerr effect systems of the prior art, it has been necessary to obtain measurements from two separate devices, one longitudinal and one transverse. Proper alignment between instruments becomes difficult, as is the ability to gauge the relative strength of the discrete applied fields.
The easy axis of a material is the axis along which the material is most readily magnetized in the presence of an externally applied magnetic field. Certain materials exhibit easy axis dispersion, where the easy axis varies from point to point across the surface of the sample. Scalar detection systems have consequently provided incomplete characterization of anisotropic materials.
A system and method for realizing vector Kerr magnetometry is disclosed. The system enables simultaneous longitudinal and transverse Kerr effect measurements at a single point on a sample surface. Consequently, anisotropic materials may be more completely, rapidly and accurately characterized. The system may be used with a variety of materials to be tested, including but not limited to magnetic media (e.g. hard drive platters), thin film heads, magnetic random access memory (MRAM) and permanent magnetic wafers.
An optional component of the presently disclosed system includes a sample platform with motive elements and an associated controller for achieving precise relocation of the sample under test in x, y, and theta. Thus, even though the present system enables two-dimensional hysteresis loop characterization at a sample location without sample movement, the repositionable platform as disclosed enables complete, 360 degree characterization about a single point, if desired. Alternatively, the highly precise control mechanisms may be utilized in obtaining longitudinal and transverse Kerr effect measurements at succeeding points on the surface of a sample. Rapid sample characterization is thus achieved, including easy axis dispersion measurement with a much higher accuracy as compared to prior art measurement systems.
A further embodiment of the presently disclosed system includes the integration of a polar Faraday effect emitter/detector pair in conjunction with the vector Kerr magnetometry system disclosed above, either with or without the x, y, and theta translatable sample platform. More accurate and rapid sample characterizations are thereby achieved.